/**
 * The reveal.js markdown plugin. Handles parsing of
 * markdown inside of presentations as well as loading
 * of external markdown documents.
 * Referred from The reveal.js markdown plugin.
 * https://github.com/hakimel/reveal.js/blob/master/plugin/markdown/markdown.js
 */
export default function( marked ) {

  const DEFAULT_SLIDE_SEPARATOR = '^\r?\n---\r?\n$',
    DEFAULT_NOTES_SEPARATOR = 'notes?:',
    DEFAULT_ELEMENT_ATTRIBUTES_SEPARATOR = '\\\.element\\\s*?(.+?)$',
    DEFAULT_SLIDE_ATTRIBUTES_SEPARATOR = '\\\.slide:\\\s*?(\\\S.+?)$';

  const SCRIPT_END_PLACEHOLDER = '__SCRIPT_END__';


  /**
   * Retrieves the markdown contents of a slide section
   * element. Normalizes leading tabs/whitespace.
   */
  function getMarkdownFromSlide( section ) {

    // look for a <script> or <textarea data-template> wrapper
    let template = section.querySelector( '[data-template]' ) || section.querySelector( 'script' );

    // strip leading whitespace so it isn't evaluated as code
    let text = ( template || section ).textContent;

    // restore script end tags
    text = text.replace( new RegExp( SCRIPT_END_PLACEHOLDER, 'g' ), '</script>' );

    let leadingWs = text.match( /^\n?(\s*)/ )[1].length,
      leadingTabs = text.match( /^\n?(\t*)/ )[1].length;

    if ( leadingTabs > 0 ) {
      text = text.replace( new RegExp('\\n?\\t{' + leadingTabs + '}', 'g'), '\n' );
    }
    else if ( leadingWs > 1 ) {
      text = text.replace( new RegExp('\\n? {' + leadingWs + '}', 'g'), '\n' );
    }

    return text;

  }

  /**
   * Given a markdown slide section element, this will
   * return all arguments that aren't related to markdown
   * parsing. Used to forward any other user-defined arguments
   * to the output markdown slide.
   */
  function getForwardedAttributes( section ) {

    let attributes = section.attributes;
    let result = [];

    for ( let i = 0, len = attributes.length; i < len; i++ ) {
      let name = attributes[i].name,
        value = attributes[i].value;

      // disregard attributes that are used for markdown loading/parsing
      if ( /data\-(markdown|separator|vertical|notes)/gi.test( name ) ) continue;

      if ( value ) {
        result.push( name + '="' + value + '"' );
      }
      else {
        result.push( name );
      }
    }

    return result.join( ' ' );

  }

  /**
   * Inspects the given options and fills out default
   * values for what's not defined.
   */
  function getSlidifyOptions( options ) {

    options = options || {};
    options.separator = options.separator || DEFAULT_SLIDE_SEPARATOR;
    options.notesSeparator = options.notesSeparator || DEFAULT_NOTES_SEPARATOR;
    options.attributes = options.attributes || '';

    return options;

  }

  /**
   * Helper function for constructing a markdown slide.
   */
  function createMarkdownSlide( content, options ) {

    options = getSlidifyOptions( options );

    let notesMatch = content.split( new RegExp( options.notesSeparator, 'mgi' ) );

    if ( notesMatch.length === 2 ) {
      content = notesMatch[0] + '<aside class="notes">' + marked(notesMatch[1].trim()) + '</aside>';
    }

    // prevent script end tags in the content from interfering
    // with parsing
    content = content.replace( /<\/script>/g, SCRIPT_END_PLACEHOLDER );

    return '<script type="text/template">' + content + '</script>';

  }

  /**
   * Parses a data string into multiple slides based
   * on the passed in separator arguments.
   */
  function slidify( markdown, options ) {

    options = getSlidifyOptions( options );

    let separatorRegex = new RegExp( options.separator + ( options.verticalSeparator ? '|' + options.verticalSeparator : '' ), 'mg' ),
      horizontalSeparatorRegex = new RegExp( options.separator );

    let matches,
      lastIndex = 0,
      isHorizontal,
      wasHorizontal = true,
      content,
      sectionStack = [];

    // iterate until all blocks between separators are stacked up
    while ( (matches = separatorRegex.exec( markdown )) != null ) {
      // notes = null;

      // determine direction (horizontal by default)
      isHorizontal = horizontalSeparatorRegex.test( matches[0] );

      if ( !isHorizontal && wasHorizontal ) {
        // create vertical stack
        sectionStack.push( [] );
      }

      // pluck slide content from markdown input
      content = markdown.substring( lastIndex, matches.index );

      if ( isHorizontal && wasHorizontal ) {
        // add to horizontal stack
        sectionStack.push( content );
      }
      else {
        // add to vertical stack
        sectionStack[sectionStack.length-1].push( content );
      }

      lastIndex = separatorRegex.lastIndex;
      wasHorizontal = isHorizontal;
    }

    // add the remaining slide
    ( wasHorizontal ? sectionStack : sectionStack[sectionStack.length-1] ).push( markdown.substring( lastIndex ) );

    let markdownSections = '';

    // flatten the hierarchical stack, and insert <section data-markdown> tags
    for ( let i = 0, len = sectionStack.length; i < len; i++ ) {
      // vertical
      if ( sectionStack[i] instanceof Array ) {
        markdownSections += '<section '+ options.attributes +'>';

        sectionStack[i].forEach( function( child ) {
          markdownSections += '<section data-markdown>' + createMarkdownSlide( child, options ) + '</section>';
        } );

        markdownSections += '</section>';
      }
      else {
        markdownSections += '<section '+ options.attributes +' data-markdown>' + createMarkdownSlide( sectionStack[i], options ) + '</section>';
      }
    }

    return markdownSections;

  }

  /**
   * Parses any current data-markdown slides, splits
   * multi-slide markdown into separate sections and
   * handles loading of external markdown.
   */
  function processSlides() {

    let sections = document.querySelectorAll( '[data-markdown]'),
      section;

    for ( let i = 0, len = sections.length; i < len; i++ ) {

      section = sections[i];

      if ( section.getAttribute( 'data-markdown' ).length ) {

        let xhr = new XMLHttpRequest(),
          url = section.getAttribute( 'data-markdown' );

        let datacharset = section.getAttribute( 'data-charset' );

        // see https://developer.mozilla.org/en-US/docs/Web/API/element.getAttribute#Notes
        if ( datacharset != null && datacharset != '' ) {
          xhr.overrideMimeType( 'text/html; charset=' + datacharset );
        }

        xhr.onreadystatechange = function() {
          if ( xhr.readyState === 4 ) {
            // file protocol yields status code 0 (useful for local debug, mobile applications etc.)
            if ( ( xhr.status >= 200 && xhr.status < 300 ) || xhr.status === 0 ) {

              section.outerHTML = slidify( xhr.responseText, {
                separator: section.getAttribute( 'data-separator' ),
                verticalSeparator: section.getAttribute( 'data-separator-vertical' ),
                notesSeparator: section.getAttribute( 'data-separator-notes' ),
                attributes: getForwardedAttributes( section )
              });

            }
            else {

              section.outerHTML = '<section data-state="alert">' +
                'ERROR: The attempt to fetch ' + url + ' failed with HTTP status ' + xhr.status + '.' +
                'Check your browser\'s JavaScript console for more details.' +
                '<p>Remember that you need to serve the presentation HTML from a HTTP server.</p>' +
                '</section>';

            }
          }
        };

        xhr.open( 'GET', url, false );

        try {
          xhr.send();
        }
        catch ( e ) {
          alert( 'Failed to get the Markdown file ' + url + '. Make sure that the presentation and the file are served by a HTTP server and the file can be found there. ' + e );
        }

      }
      else if ( section.getAttribute( 'data-separator' ) || section.getAttribute( 'data-separator-vertical' ) || section.getAttribute( 'data-separator-notes' ) ) {

        section.outerHTML = slidify( getMarkdownFromSlide( section ), {
          separator: section.getAttribute( 'data-separator' ),
          verticalSeparator: section.getAttribute( 'data-separator-vertical' ),
          notesSeparator: section.getAttribute( 'data-separator-notes' ),
          attributes: getForwardedAttributes( section )
        });

      }
      else {
        section.innerHTML = createMarkdownSlide( getMarkdownFromSlide( section ) );
      }
    }

  }

  /**
   * Check if a node value has the attributes pattern.
   * If yes, extract it and add that value as one or several attributes
   * the the terget element.
   *
   * You need Cache Killer on Chrome to see the effect on any FOM transformation
   * directly on refresh (F5)
   * http://stackoverflow.com/questions/5690269/disabling-chrome-cache-for-website-development/7000899#answer-11786277
   */
  function addAttributeInElement( node, elementTarget, separator ) {

    let mardownClassesInElementsRegex = new RegExp( separator, 'mg' );
    let mardownClassRegex = new RegExp( "([^\"= ]+?)=\"([^\"=]+?)\"", 'mg' );
    let nodeValue = node.nodeValue;
    let matches = mardownClassesInElementsRegex.exec( nodeValue );
    if ( matches != null ) {

      let classes = matches[1];
      nodeValue = nodeValue.substring( 0, matches.index ) + nodeValue.substring( mardownClassesInElementsRegex.lastIndex );
      node.nodeValue = nodeValue;
      let matchesClass;
      while ( (matchesClass = mardownClassRegex.exec( classes )) != null ) {
        elementTarget.setAttribute( matchesClass[1], matchesClass[2] );
      }
      return true;
    }
    return false;
  }

  /**
   * Add attributes to the parent element of a text node,
   * or the element of an attribute node.
   */
  function addAttributes( section, element, previousElement, separatorElementAttributes, separatorSectionAttributes ) {

    if ( element != null && element.childNodes != undefined && element.childNodes.length > 0 ) {
      let previousParentElement = element;
      for ( let i = 0; i < element.childNodes.length; i++ ) {
        let childElement = element.childNodes[i];
        if ( i > 0 ) {
          let j = i - 1;
          while ( j >= 0 ) {
            let aPreviousChildElement = element.childNodes[j];
            if ( typeof aPreviousChildElement.setAttribute == 'function' && aPreviousChildElement.tagName != 'BR' ) {
              previousParentElement = aPreviousChildElement;
              break;
            }
            j = j - 1;
          }
        }
        let parentSection = section;
        if ( childElement.nodeName ==  'section' ) {
          parentSection = childElement ;
          previousParentElement = childElement ;
        }
        if ( typeof childElement.setAttribute == 'function' || childElement.nodeType == Node.COMMENT_NODE ) {
          addAttributes( parentSection, childElement, previousParentElement, separatorElementAttributes, separatorSectionAttributes );
        }
      }
    }

    if ( element.nodeType == Node.COMMENT_NODE ) {
      if ( addAttributeInElement( element, previousElement, separatorElementAttributes ) == false ) {
        addAttributeInElement( element, section, separatorSectionAttributes );
      }
    }
  }

  /**
   * Converts any current data-markdown slides in the
   * DOM to HTML.
   */
  function convertSlides() {

    let sections = document.querySelectorAll( '[data-markdown]');

    for ( let i = 0, len = sections.length; i < len; i++ ) {

      let section = sections[i];

      // Only parse the same slide once
      if ( !section.getAttribute( 'data-markdown-parsed' ) ) {

        section.setAttribute( 'data-markdown-parsed', true );

        let notes = section.querySelector( 'aside.notes' );
        let markdown = getMarkdownFromSlide( section );

        section.innerHTML = marked( markdown );
        addAttributes(   section, section, null, section.getAttribute( 'data-element-attributes' ) ||
                section.parentNode.getAttribute( 'data-element-attributes' ) ||
                DEFAULT_ELEMENT_ATTRIBUTES_SEPARATOR,
        section.getAttribute( 'data-attributes' ) ||
                section.parentNode.getAttribute( 'data-attributes' ) ||
                DEFAULT_SLIDE_ATTRIBUTES_SEPARATOR);

        // If there were notes, we need to re-add them after
        // having overwritten the section's HTML
        if ( notes ) {
          section.appendChild( notes );
        }

      }

    }

  }

  // API
  return {
    getMarkdownFromSlide: getMarkdownFromSlide,
    createMarkdownSlide: createMarkdownSlide,
    processSlides: processSlides,
    addAttributes: addAttributes,
    convertSlides: convertSlides
  };
}
